1. Technical Field
The present invention relates to a pressure sensor device.
2. Related Art
In recent years, integration between Micro Electro Mechanical System (MEMS) and IC has been progressed in the silicon industry, and various types of complex semiconductor devices have been developed. As examples of such devices, in particular, acceleration sensors, gyro sensors, resonators as timing devices, and so on have been developed energetically. Further, there are still a lot of problems remaining in fusion and integration between MEMS devices and Complementary Metal Oxide Semiconductor (CMOS), and various engineering developments are in progress.
In the past, as a pressure sensor for detecting pressure, there have been generally used a capacitance type pressure sensor, a piezoresistive sensor, a piezoelectric sensor, and so on, and in particular, those called a piezoresistive sensor have become mainstream (see e.g., JP-A-7-27643).
Here, as a pressure sensor 100 shown in FIG. 15A for example, since the capacitance type pressure sensor is provided with a configuration in which a diaphragm 101 with a certain gap is disposed so as to move in accordance with a pressure difference, and the capacitance variation thereof is detected, the power consumption required for operation thereof is small. Therefore, the capacitance type pressure sensor is particularly used for applications requiring low power consumption. However, since such a capacitance type pressure sensor has low sensitivity, in order for achieving the sensitivity higher than a certain level, the diaphragm 101 needs to have a large area, and at the same time, the structure needs to become complicated. Therefore, if it is attempted to apply the capacitance type pressure sensor 100 shown in FIG. 15A in the MEMS field, for example, there arises a problem that it is difficult to integrally form the capacitance type pressure sensor and a CMOS circuit or the like, for detecting the pressure applied to the pressure sensor, with each other.
Further, as pressure sensors 110, 120 shown, for example, in FIGS. 15B and 15C, the piezoresistive pressure sensor has a structure in which bridge resistors 112 disposed on semiconductor thin films 111, 121 are distorted in response to the pressure applied thereto, and the variation in resistance on this occasion is converted into a voltage and then detected, and has high sensitivity. Further, in the case of application to the MEMS field described above, it is possible to easily integrate the pressure sensor and the CMOS circuit or the like with each other. However, in such piezoresistive pressure sensors 110, 120, since it is required to continuously supply the bridge resistors 112 with a constant current flow, there arises a problem that it is not suitable for applications requiring low power consumption. In particular, since it is required to add another constant current circuit in order for reliably improving the operational accuracy in a high temperature range, there is a problem of incurring a further increase in current consumption.
Further, the piezoelectric pressure sensor has a structure in which a piezoelectric film, which is disposed on a diaphragm formed of a silicon substrate formed to be a thin film, is distorted in response to the pressure applied thereto, and the voltage variation on this occasion is detected, and has low power consumption. Further, in the case of application to the MEMS field described above, it is possible to easily integrate the pressure sensor and the CMOS circuit or the like with each other. However, the piezoelectric pressure sensor in the related art has low sensitivity in pressure detection, and has a problem that it is difficult to use the piezoelectric pressure sensor for applications requiring detection of a particularly small pressure variation.
Therefore, a pressure sensor (a pressure sensor device), which can easily be formed integrally with a semiconductor circuit such as a CMOS circuit, which has low power consumption, and which is superior in pressure detection sensitivity, is desired.